Neither http://mongodb.github.io/mongo-csharp-driver/2.1/reference/bson/mapping/polymorphism/ nor http://mongodb.github.io/mongo-csharp-driver/2.1/reference/bson/mapping/conventions/ mention the correct way to register a DiscriminatorConvention. This led me to try adding a ScalarDiscriminatorConvention to a ConventionPack, which doesn't work – and I had to [ask a question on Stack Overflow](http://stackoverflow.com/q/33432899/2314532) before I could figure out how to register a DiscriminatorConvention properly. (My database used a field called "type" rather than "_t", hence my need for a different discriminator convention.)

The reference documentation should probably be updated to mention this scenario, so that anyone else with similar needs will know how to do it in the future.